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M. Di Martino (Torino Observatory, Italy), J. Oberst, S. Mottola (DLR, Berlin, Germany), DS1 Science Team
Little is known about the small Mars crosser asteroid 9969 (1992 KD), which was recently chosen as a target for the DS1 mission. In order to obtain additional data on the physical properties of this object, we have carried out a coordinated photometric observing campaign using telescopes based in Mount Stromlo (Australia) and El Leoncito (Argentina) observatories. We find that the object's brightness varies by up to 0.5 mag from night to night, while there is probably also significant variation of 0.2 mag within individual nights. Assuming that the asteroid has a two-maxima/two-minima lightcurve, the most probable synodic rotational period is 226 +/- 3 hours (9.4 days) with a mean lightcurve magnitude R(1,a=24)=17.0 and a peak-to-peak amplitude of about 0.9 mag. However, for rotational periods of this length, we should expect the asteroid to be in an excited rotation state, owing to the long damping time required for this small object to return to principal-axis rotation (Harris, Icarus 107, 209-211, 1994). As in the case of 4179 Toutatis, the object may show a very complex lightcurve. Assuming that the albedo of this presumed S-type asteroid (Hicks et al., Lunar Planetary Science, 1999) is near 25 2 km. The high lightcurve amplitude suggests that 1992 KD has a very elongated shape with a/b > 2. Further observations are required to refine the asteroid's rotational model, which currently does not even reliably predict its rotational phase during the time of the DS1 flyby. As precise photometric observations are currently difficult (the asteroid is visible only under high airmass), further analyses must probably await new opportunities for observations (requiring 3-m class telescopes) beginning in October 2000.
The author(s) of this abstract have provided an email address for comments about the abstract: dimartino@to.astro.it